Two dukes in auction for land (6)
I believe the answer is:
saddle
'for land' is the definition.
(I've seen this before)
'two dukes in auction' is the wordplay.
'two dukes' can mean two replacements for 'duke'.
'duke' becomes 'd' (abbreviation).
'duke' becomes 'd' (abbreviation).
'in' indicates putting letters inside.
'auction' becomes 'sale' (I've seen this in other clues).
'd'+'d'='dd'
'dd' going into 'sale' is 'SADDLE'.
(Other definitions for saddle that I've seen before include "Chafed by riding" , "load" , "Equestrian equipment" , "Cycle seat" , "Seat for a rider, horse or bike" .)